Studies On The Starch-Like Granules Co-Accumulated With Polyhydroxybutyrate In Spirulina Platensis
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Date
2007-06
Authors
Peng, Yew Saw
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Abstract
Spirulina platensis is capable of synthesizing small amount of
polyhydroxyalkanoate (PHA) under nitrogen starvation condition. Gas
chromatography (GC) analysis revealed that about 10 % PHA of the cell dry
weight (COW) was accumulated under mixotrophic culture condition containing
0.5% (w/v) of sodium acetate. However, Nile blue A stained cells showed the
presence of large quantities of granules in the cell cytoplasm when viewed under
fluorescent microscope. The qualitative observation was in contrast to the
quantitative GC analysis which suggested that not all the fluorescent granules
are PHAs. It was hypothesized that S. p/atensis co-accumulated other storage
products that were stained with Nile blue A along with PHA under nitrogen
starvation condition. Closer observation by transmission electron microscopy
(TEM) revealed the presence of starch-like granules along with PHA granules.
Analysis of several types of commercial starches confirmed that starch granules
could be stained by Nile blue A although the intensity of the fluorescence was
lower than for PHA granules. In order to further characterize the starch-like
granules, large genomic DNA fragments of S. platensis were randomly cloned
into E. coli 817-1 and resulting recombinants were screened for Nile blue A
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positive characteristic. One such recombinant E. coli was able to accumulate
morphologically similar granules. GC and PHA synthase activity analyses
confirmed that these are not PHA granules. GC-MS analysis revealed that the
recombinant E. coli accumulated starch-like compound consisting of glucose
monomers. The granules exhibited birefringence under polarized light, which is a
characteristic of semi-crystalline starch granules. This study showed for the first
time that S. platensis co-accumulated PHA and starch-like granules during
nitrogen starvation. Suppression of the starch-like granule biogenesis might
produce a higher PHA accumulation in S. platensis.
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Keywords
Spirulina Platensis